The instant invention relates to a method of producing silicon-on-insulator (SOI) material. Such a material is particularly adapted for use in integrated circuit applications, such as high voltage integrated circuits where both the dielectric isolation and availability of a wide range of semiconductor thicknesses are desirable.
It is known that SOI material may be produced by the "direct silicon bonding technique". In this method, two silicon wafers are joined together to form a strong bond and then one of the wafers is thinned to desired thickness.
J. B. Lasky, Appl. Phys. Let. 48, 78 (1986) discloses such a technique. In the Lasky process, two polished Si wafers the surface of one of which or both of which may be coated with the film of silicon dioxide, are contacted to form a bonded pair. One wafer of the pair is referred to as the "handle" wafer and the other as the "device" wafer. The SOI material of the desired thickness is then obtained by thinning the device wafer to the desired thickness.
An etching technique for thinning the device wafer is shown in Maszara et al, J. Appl. Phys. 64 (10), 4943 (1988). In the method shown in the Maszara et al article, after bonding together the device and handle wafers, an ion-implanted boron doped layer is employed as an etch stop, and the device wafer is thinned down by selective chemical etching. This method results in the formation of SOI layers having a silicon layer of a thickness of 30 nm-700 nm with a thickness uniformity of .+-.20 nm. However, due to the high boron implant doses necessary for the production of an effective etch stop, implant damage in the form of a high density of dislocations is produced in the final SOI material.
Another method of producing an SOI film of the desired thickness consists of grinding and polishing of the device wafer, described in Electrochem Soc. Proc., Vol. 90-6, p. 61, 1990. By this method, SOI layers of a thickness of 2 microns and above with a tolerance of 0.5 microns for a thickness of 2-3 microns have been produced. However, attempts to produce an SOI layer by mechanical grinding and polishing with a better thickness tolerance have not proved to be successful.